How to change the date format in the date field as a select list?

Question

On user registration page, I have added a date field in select list.

In the manage form display tab, I can set the order of the dropdown fields like day/month/year or month/day/year But I am unable to change the format of the date.

Currently in the day dropdown, it is displaying like 1, 2, 3 and I want to change it to 01, 02, 03. Similarly in the month dropdown, it is displaying like, Jan, Feb and I want to display it like January, February.

Is this possible?

Answer 1

If you want to alter the way this component is shown globally, you can implement hook_preprocess_datetime_form(), eg. like this:

function mymodule_preprocess_datetime_form(&$variables) {
  // Ensure there's a month field and it's a select.
  if (isset($variables["content"]["month"]) && $variables["content"]["month"]['#type'] === 'select') {
    foreach ($variables["content"]["month"]['#options'] as $monthNum => $label) {
      if ($monthNum) {
        // Convert month number to unabbreviated name.
        $dateObj = DateTime::createFromFormat('!m', $monthNum);
        $monthName = $dateObj->format('F');
        $variables["content"]["month"]['#options'][$monthNum] = $monthName;
  }
}

}

The code for the day select will be similar.

Answer 2

Use hook_form_FORM_ID_alter():

/**
 * Implements hook_form_FORM_ID_alter().
 */
function <your_module>_form_user_register_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  // your custom code here
}

You'll need to set the #date_format for your custom date field in the form array.

This entry in the Drupal.org community documentation might help you with that.

The PHP documentation for date formats may also be helpful here.